Well first off, welcome to the WoW RP scene!
As far as joining a guild, I highly recommend taking your time and shopping around. See who’s hanging out in game -especially in WrA-Horde RP hotspots like the Valley of Honor and Silvermoon- during the hours you’re most active.
Here’s a list of guilds recruiting. Part of the huge sticky at the top of the WrA forum.
https://us.forums.blizzard.com/en/wow#HordeGuilds
And I’d be failing at my job if I didn’t get in a plug for my own guild home- Firebrand Enterprises!
We’ve been getting a couple of people who’re dipping their toes into RP as a way to stay engaged in WoW during the current content slump, and it’s been fun helping them learn the ropes!